import java.util.Scanner;

public class Test2 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int n = in.nextInt();
            int[] prices = new int[n];
            for (int i = 0; i < n; i++) {
                prices[i] = in.nextInt();
            }
            int minPrice = prices[0];
            int count = 0;
            for (int i = 1; i < n; i++) {
                if (prices[i] > minPrice) {
                    count += (prices[i] - minPrice);
                    minPrice = prices[i];
                } else {
                    minPrice = Math.min(minPrice, prices[i]);
                }
            }
            System.out.println(count);
        }
    }
}
